This invention relates generally to machines adapted for testing lubrication and material wear properties. More specifically, the invention relates to machines of the type having wear specimens, also known as bearing blocks, disposed on either side of a rotating pin, and adapted to apply radial inwardly directed pressure onto the pin for wear and lubrication testing purposes.
One such test machine is disclosed in M. Cornell, U.S. Pat. No. 2,110,288, and certain associated test methods are disclosed in F. A. Faville, U.S. Pat. No. 2,106,170 and F. A. Faville, U.S. Pat. No. 3,190,109. Standardized tests for such machines are included in ASTM D 2670-88, Measuring Wear Properties of Fluid Lubricants; ASTM D 3233-93, Measurement of Extreme Pressure Properties of Fluid Lubricants; and ASTM D 2625-90, Endurance (Wear) Life and Load-Carrying Capacity of Solid Film Lubricants.
In machines of this general type, loading jaws or bearing block holders located on either side of the pin are formed with bores extending radially therefrom. A set screw is threaded into the outer ends of the bores, the bearing blocks are slidably received into the inner ends of the bores, and a load transferring ball is located between the set screw and the be ring block. The end of the bearing block adjacent the ball is formed with a conical depression or dimple for receiving the ball in axial compressive load carrying contact. The opposite end of the bearing blocks are formed with wear surfaces that define a V-shaped notch for receiving and establishing line bearing contact with the pin.
During testing, a force application mechanism moves the bearing block holders inwardly toward the pin. When the blocks are in contact with the rotating pin, the force from the mechanism is transferred from the bearing block holder to the bearing block via the ball in force transferring contact therewith. During such testing, the bearing surfaces of the V-shaped notch experience wear resulting from the pressure applied to the rotating pin by the bearing blocks. Therefore, prior bearing blocks of this type must typically be replaced after each test.
Studying the wear patterns and measuring the depth of wear on the bearing or wear surfaces of such prior bearing blocks presents difficulties because of the presence of the adjacent wear surface defining the V-shaped notch.
In addition, testing relatively soft materials with such prior bearing blocks presents difficulties. If the blocks are formed from the soft material, the block will likely undergo deformation due to compressive forces and the length of the material of the bearing block between the ball and the pin. With conventional testing machines, this compression will result in substantial changes in the force applied by the loading mechanism, and require careful vigilance of the operator to compensate for the loss in applied force. The outwardly directed force component due to the force transmitting relation of the ball acting against the angled surface of the conical depression in the bearing block results in further deformation of the specimen. Quit simply, prior bearing blocks made from soft materials will typically not hold their. shape sufficiently to provide meaningful wear data.